The invention relates to a variable control of the gas exchange in internal combustion engines. The term xe2x80x9cgas exchangexe2x80x9d characterizes the periodic exchange of the cylinder charge, that is, the discharge of exhaust gas and the inflow of an air/fuel mixture. In conventional internal combustion engines, the gas exchange control takes place via spring loaded valves which are opened by a camshaft. The opening function as a time-dependent trace of the valve opening (that is, start, duration and extent of the opening cross section) is determined by the form of the camshaft. In conventional engines, the opening function can therefore be very precisely determined by the shape of the camshaft but is not variable. Other systems are known for controlling the gas exchange with variable opening function. U.S. Pat. No. 4,957,074 discloses electromagnetically controlled and hydraulically actuated valves having variable opening function. To eliminate the effects of tolerances and deterioration in the actuation of the valve, the valve stroke is detected by a valve stroke sensor and the detected value is considered when driving the valve. What is problematic here is the allocation of the signal of the valve stroke sensor to the actual valve stroke. For example, offsets can occur in the sensor signal which make a correct allocation difficult. To alleviate this situation, the valve stroke sensor of U.S. Pat. No. 4,957,074 is calibrated after each closing operation. For this purpose, the valve stroke sensor signal is arbitrarily set to zero when there is a missing valve opening signal. This calibration is correct when the valve is actually closed and this applies when the actuation is intact and the opening signal is missing. In cases wherein the valve does not close in a defective manner, this calibration, however, leads to an incorrect zero point adjustment of the valve stroke sensor.
DE 195 01 386 discloses a variable valve control wherein the opening function of the gas exchange valves is determined by an opening camshaft and a closing camshaft. The opening function can be varied within wide limits via a change of the phase shift between the shafts rotating with the same rotational frequency. The phase shift is changed via a coupling mechanism. In this system, an angle transducer in the valve actuation mechanics can detect the actual movement of the valves or of the valve actuating elements.
Here, the problem arises to allocate the position of the angle transducer to the position of the inlet valves which are opening.
The object of the invention is the provision of an arrangement which supplies a clear allocation between the start of the opening of the inlet valves and the signal of a valve stroke sensor or angle transducer.
In detail, the following takes place in the control of the gas exchange valves of an internal combustion engine:
the control is variable and makes possible to completely hold closed at least the inlet valves;
the formation of a signal which indicates the air quantity inducted by the engine;
a detection of an index for the valve position;
an opening drive of at least one inlet valve in overrun operation proceeding from completely holding closed the inlet valves;
a detection of the index of the detected valve position wherein a reaction of the signal occurs as a function of the air quantity and a use of this index as a reference point for determining the actual valve position.
The invention thereby makes possible a clear allocation of the signal of a valve stroke sensor to the actual position of the opening inlet valves. This is made possible by a comparison of the signal of the air mass sensor with the signal of the valve stroke sensor. As long as the air mass sensor indicates an air mass flow unequal to zero, a valve lifting is given. In overrun operation wherein no engine torque is needed, the inlet valves can be completely closed so that the engine does not induct any fresh air and the air mass sensor indicates the value zero. Via a test function, the opening signal of the inlet valve for an adequately long overrun operation can be successively increased from the value zero in the direction of inlet valve opening. For an opening signal wherein there occurs, for the first time, a transition from the air mass signal which is constant at zero to a pulsating very low air mass flow, the start of the valve lifting is present. All other valve stroke sensor signals can refer to the signal of the valve stroke sensor occurring at this event.
In this way, the invention makes possible an automatic calibration of a valve stroke sensor or an angle transducer in the valve actuating mechanics. In this way, the necessity of a complex adjustment of the sensor or angle transducer during assembly is unnecessary. Furthermore, the automatic calibration minimizes the requirements as to the tolerances of the sensors.
In one embodiment, the formation of a signal (which indicates the air quantity inducted by the engine) takes place such that the signal of an air mass sensor is averaged over a crankshaft angular region b about the start of a valve lifting which region b is less than the spacing between two sequential ignitions in the engine.
This leads to the advantage of an increased measuring accuracy of the teaching of the invention. This procedure is especially advantageously to be achieved in a throttle-free charge control via the inlet valves (without throttle flap).
The increased sensitivity furthermore permits a detection of smaller pulsations and also a detection of cylinder-specific differences at the start of the valve lifting.
Of special advantage is furthermore the possibility of the diagnosis of the inlet valves as to tight closure. This permits the detection of starting leakages as they are caused, for example, by a valve play which is too little. An indication and/or storage of this fault permits an early correction of the valve play either via an automatic intervention of the electronic valve control or via a visit to a service facility. Costly damage because of burning of the valves as a consequence of deficient heat conduction away via the valve seat can be avoided in this manner.